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What is the method to calculate a finite wing's lift from its sectional airfoil shape?
I am struggling to get my head around a concept that I believe should be fairly simple to understand.
Lift versus drag and AoA data of many airfoils are freely available, for instance the NACA 4-digit airfoils.
The data is that of sectional, or 2D, lift and drag, or $C_l$ and $C_d$.
Now, if I were to build a 3D finite wing using a certain airfoil, how would I go about calculating the 3D coefficient of lift $C_L$?
I know that the aspect ratio $AR$ and Oswald efficiency factor $e$ come into play and that $C_D<C_d$ because of 3D effects such as tip leakage.
As an example, let's look at the NACA2412 airfoil: At $\alpha=8$ and at $Re=5.7e6$, it experiences $C_l=1$.
If I now manufacture a wing of $AR=7$ which has a planform giving an efficiency $e=0.8$, how would I go about calculating $C_L$?
Are there any exact methods to calculate this or perhaps approximations?

2D is a simplification of real life... it's very difficult to translate something 2D to something 3D. However there are approximations but I can tell you that no exact method is available.
One of the key components of drag that you are missing in 2D is the induced drag, which is the drag generated by a wing simply because it has a finite dimension. The difference in circulation created by each airfoil has an influence over the complete wing.
There is a theory which is linear and non-viscous that helps to compute the aerodynamic components of the wing, based on the aerodynamic characteristics of the airfoils the wing is made of. It also allows you to create twist. It is subject to simplifications such as as being linear and missing viscosity, but it provides a very good approximation for the effort (analytical for a significant amount of cases, and excel does the work for others).
The theory is the lifting-line theory and what you just need to is: add the induced drag provided by the theory (you don't have it in your airfoil):
$\ C_{D_i} = \frac{{C_L}^2}{\pi \text{AR} e} $
You need to know the planform for being able to make the integral of your wing, but the following equation will save you some time:
$ \ C_{L3D} = C_{l_\alpha} \left( \frac{\text{AR}}{\text{AR}+2} \right) \alpha$

Thank you very much. For interests sake, if you wrap the latex in $`s the equations will be displayed properly! One thing I have also wondered : If one of the ways of thinking about induced drag is seeing it as the component of lift acting parallel to the free stream, then why is induced drag not present in 2D? Because in 2D you also have this component of lift acting parallel to the free stream.

@Jonny thanks for the hint of $, changed now. What it is happening is that in a wing there is a difference between one airfoil and the next, specially in size. That makes a difference in the pressure between both, when you have a gradient, the air moves in that direction. Essentially, induced drag is the air moving along the span of the wing trying to turn back from lower to upper side. It is called "induced" because it is seen by each airfoild as an angle of attack induced by the wing.

Thank you, do you have a reference for the equation of 3D lift you supplied above?

Yes, is the link that I have included (basically wikipedia, but you can google easily lifting line theory and you will find). If I remember well, there is a complex math theorem you need to use to obtain the formulae.

Will do. Cheers!

Good! If this theory is not enough for you, try to look in ESDU for a semi-empirical description of your wing or go to panel methods (really light CFD)

I assume that the approximating formula for CL3D does not take flaps into account, as it only uses the airfoil's lift slope, which should stay constant when flaps are applied?

@Jonny: Induced drag is not present in 2D because with an infinite aspect ratio the wing will create infinite lift even at very small angles of attack. Since induced drag is the consequence of the wing deflecting the oncoming airflow downwards, an infinitesimally small deflection is needed to produce infinite lift.

@Jonny in the lifting-line theory the flaps are just a different airfoil section, however, will change the section making you make the complete integral as you will not have an analytic solution.

@TrebiaProject. It seems like the C_L3D approximation just scales the lift coefficient of a thin foil by AR/(AR+2). Would it then be appropriate to approximate the 3D lift coefficient for a chambered foil by doing the scaling the same way?

The Cl_alpha that you need to introduce is the one given by the corresponding 2D theory. So yes for the chambering and also the Prandlt-Glauert theory for example.

The analytical solution I provided assumes uniform airfoil shape, if it is not uniform you need to use some integrals... usually the wing manufacturer is providing the  aspect ratios...

So just to be verbose, I can scale the 2d Lift coefficient of a chambered foil by (AR/(AR+2)) to get a better approximation for the 3d lift coefficient? Or do i need to compensate for the angle of attack, and find some other C_Lalpha?

Yes you can, with the limitations of the theory. It's not valid for maximun CL alpha, no viscous effects are taken into account (which is valid in linear range) and all the airfoild must be identical.

There are indeed several approximations, depending on the shape of the wing. Generally, the lift curve slope is $2\pi$ only for a flat plate in inviscid 2D flow (with Kutta condition fulfilled). With thicker airfoils, the lift curve slope in 2D increases slightly. It also increases with Mach number proportional to the Prandtl-Glauert factor $\frac{1}{\sqrt{1-Ma^2}}$ and the Reynolds number.
Now to 3D flow: Once you move away from infinite aspect ratios, the lift curve slope drops. With very small aspect ratios $AR$ the lift curve slope becomes $c_{L\alpha} = \frac{\pi \cdot AR}{2}$. See the plot below for the ideal lift curve slope of an unswept wing:

Please note that the red line is only valid for AR = 0! Then the lift curve slope increases up to $c_{L\alpha} = 2\cdot\pi$  for $AR = \infty$ (and zero airfoil thickness and no friction effect), as shown by the blue line. If you know your airfoil lift curve slope, modify the result from the plot above by the ratio between the airfoil lift curve slope and $2\pi$. Now your lift coefficient will become:
$$c_L = c_{L\alpha_{3D}}\frac{c_{L\alpha_{2D}}}{2\pi}\cdot\alpha$$
with your angle of attack $\alpha$ in radians.
For an analytic approach you may use the formulas below, but stay away from the region close to Mach 1. If those (rather precise) approximations look too daunting, feel free to simplify them:

Nomenclature:
$c_{L\alpha} \:\:$ lift coefficient gradient over angle of attack
$c_{L\alpha\:inc}$ lift coefficient gradient over angle of attack in incompressible flow
$\pi \:\:\:\:\:$  3.14159$\dots$
$AR \:\:$  aspect ratio of the wing
$\nu \:\:\:\:\:$  the wing's dihedral angle
$\varphi_m \:\:$  sweep angle of wing at mid chord
$\varphi_{LE} \:$  sweep angle of wing at leading edge
$\lambda \:\:\:\:\:$  taper ratio (ratio of tip chord to root chord)
$(\frac{x}{l})_{d\:max} \:$  chordwise position of maximum airfoil thickness
$Ma \:\:$  Mach number

Note that you do not need the planform efficiency (Oswald factor) $\epsilon$ for calculating lift curve slope. That only comes into play when you compute the [induced drag][4] of the wing.

Do you have a source for those equations in your table? Just curious, as I want to learn more about that. Thanks for the answer.

@Gus: Here is a good primer with increasingly complex equations the more effects are included. To be honest, the top one I composed myself. Try this for highly swept wings

Thanks — the $c_{L α ic}$ term in that second equation is still confusing me, though.  I understand that term is the incompressible lift coefficient for a finite wing over angle of attack — is there a good resource explaining how one can compute this for a given wing? I'm having trouble finding anything in my textbook or online.

Also, I think that formula for lift curve slope of a supersonic leading edge is wrong. That's saying lift curve slope drops as AR grows, which is at odds with other forms I've seen, e.g. here (search page for Hoerner and Borst). I'm guessing there's just a typo in your image?

@Gus: Yes, you are right. Found it on page 17-14 of FDL. Corrected. The formula for the subsonic delta wing uses the Polhamus correction factor for nose thrust. That is described in NASA TP 1500, but I think I have the formula from a software that used information from that paper.

Great, thanks Peter!


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What is the explanation for the different lines in the payload/range diagram for the Airbus A320?
In the A320-200's 'AIRCRAFT CHARACTERISTICS AIRPORT AND MAINTENANCE PLANNING' document. It presents the A320's PL/R capabilities as:

Firstly, I would like to know: What are the 3 different MTOW's listed? Is it for different seating layouts? eg 'high density' vs 'business + economy' or what? Note that 73.5(78) tonnes is the MTOW listed on Airbus's website, seen here, but they don't clearly indicate what the figure in brackets indicates.
Secondly, does the payload axis include passengers as well as cargo? If so, if the maximum amount of passengers is listed as 180, how much additional cargo can the aircraft carry, both in the cargo hold and overhead luggage trays? i.e. what model does the airlines/airframers use to estimate the weight of 180 passengers?

Passengers are sometimes referred to as self-loading cargo, so yes cargo includes them

There are two different Maximum Take Off Masses (MTOM) listed in the graph: 73.5 T and 78 T. This is only a small selection. The Airbus A320 has many variations due to modifications to fuel tanks, fuselage, engines, wings and landing gear. The following MTOMs have been certified (EASA PDF): 66 T, 67 T, 68 T, 70 T, 71.5 T, 73.5 T, 75.5 T, 77 T and 78 T.
In addition to the variation in MTOM, there are variations in the number of fuel tanks installed. The A320-100 series have either 2 or 3 tanks, while the A320-200 series can have up to 5 tanks. More fuel tanks allow an increase in range at the cost of payload. Even on short flights additional tanks will decrease the maximum payloads due to their structural weight. The brown line in the chart represents an A320 with one Additional Centre Tank (ACT) installed.
Payload includes passengers as well as cargo. Assuming an average adult weight of 88 kg (EASA PDF) including carry-on luggage, 180 passengers weigh 15840 kg. Depending on the variant of A320 you take, that leaves a couple of tonne margin for other payload such as check-in luggage or fuel to increase the range.
For more on estimating aircraft loading, see this question.

Do you know why they would only show the diagram for those 3 variants? Are they perhaps the most common?

@Jonny The 73.5 T variant is the basic A320. The 78 T is the current high gross weight model. The previous HGW MTOM was 77 T. I don't know about all the other models but I expect there are some special short field models in there with reduced take-off weights.

@DeltaLima: There are at least several variants with more powerful engines. These are primarily for hot-and-high operations, but it affects MTOM too.

@JanHudec Indeed the MTOM is affected by the engine type. But apart from engine types there are other modifications that impact the MTOM and other masses. For example the A320-211/A320-212/A320-231 (covering 4 engine types) have 17 weight variants.

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Is ultrasonic noise from small turbines painful to pets?
A question on another SE site prompted me to search for 'Aircraft engines untrasonic noise dogs', but with not much success.  The OP's dog barked like crazy at turboprops, but was not bothered at all by 'louder' noises from light GA planes with piston engines, even when led next to them as the engines ran up on the ground.
Does anyone know how much ultrasonic noise does a small turboprop put out?  I suspect that it may be worse, in proportion, to that from the large turbofans on airliners since the hp shaft revs so high on those little engines.
Maybe that noise that is merely an annoyance to humans is actually painful to dogs etc?

Unfortunately, I'm only a software engineer with a liking for dogs.

The question is also then if the dogs are barking because it's loud/painful, or it sounds like a howl (e.g. sirens), so they're responding to that.

Your dog might hate electric vehicle and induction cooker, too, together other modern "quite" high power electric equipment. They are all designed to operate at a frequency to appear to be quite to humans only, e.g. 20-40kHz range, and 25kHz is a common choice.

I don't expect that the dogs can sense the electromagnetic field, so the only audio outputs would be magnetostrictive etc. vibrations from inductors and the like.  Probalby not vey loud, (?)  Gas turbines, however, have little, if any, EM radiation, but a LOT of sound emissions.

You often hear switched mode power supplies drop into the audible range when under light load. Not very loud but nevertheless highly irritating.

@MartinJames I'm a software engineer too, and I find myself saying 'unfortunately' a lot also. Lol I wonder why that is.

@DaveDev it's one of those 'go-to' words in Friday afternoon [lack of] progress review meetings:)

How could it already be Friday afternoon for you? I'm Melbourne, Australia and it's only 9:25 am here.

You might want to try searching for "aircraft engines ultrasonic noise dogs", rather than "untrasonic"... ;-P

This answer lists a number of RPM values for different aircraft engines. A typical small turboprop engine, the PT6, runs its core at 45,000 RPM and the power turbine at 30,000 RPM, which should produce sounds in the ultrasonic region.
The picture below shows a cutaway of a PT6 (source); if you count the blades and take the result times 3 (the cutaway spans 120°), the high pressure turbine disc shows 54 blades and the power turbine 42 blades.

Each time one of those blades runs through the wake of a stator blade ahead of it, it will create a pressure change with a frequency of 30,000·42/60 = 21 kHz and 45,000·54/60 = 40.5 kHz. At idle power, the speed is a bit lower, but not by much.
So, yes, the dog might very well have heard a noise inaudible to humans.

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What is the maximum altitude allowed to fly a model plane/helicopter in England?
What is the maximum altitude I'm allowed to fly a model plane or helicopter in England?

According to the UK CAA, a model aircraft is defined as:

any ‘Small Unmanned Aircraft (SUA)’ (0-20 kg) used for sporting and
  recreational purposes and a ‘large model aircraft’ is defined as any
  ‘Unmanned Aircraft’ (over 20 kg) used for sporting and recreational
  purposes.

The following rule applies to all "small unmanned aircraft", i.e. up to 20kg:

(3) The person in charge of a small unmanned aircraft must maintain
  direct, unaided visual contact with the aircraft sufficient to monitor
  its flight path in relation to other aircraft, persons, vehicles,
  vessels and structures for the purpose of avoiding collisions.

The following rule applies between 7kg and 20kg only:

The person in charge of a small unmanned aircraft which has a mass of
  more than 7 kg excluding its fuel but including any articles or
  equipment installed in or attached to the aircraft at the commencement
  of its flight, must not fly the aircraft:
(a) in Class A, C, D or E airspace unless the permission of the
  appropriate air traffic control unit has been obtained;
(b) within an aerodrome traffic zone during the notified hours of
  watch of the air traffic control unit (if any) at that aerodrome
  unless the permission of any such air traffic control unit has been
  obtained; or
(c) at a height of more than 400 feet above the surface unless it is
  flying in airspace described in sub-paragraph (a) or (b) and in
  accordance with the requirements for that airspace

So in theory, a model aircraft weighing less than 7kg could be flown to any altitude, with the only limitation being the requirement to keep in it sight. From 7kg to 20kg the altitude is 400ft, unless you meet the airspace requirements. In practical terms, the requirement to keep the aircraft in sight "unaided" is the main limitation and that restricts the altitude of smaller models in particular.
If it's over 20kg, the model aircraft is subject to all the regular UK aviation rules but in practice a written exemption is required:

Large model aircraft having a mass between 20 kg and 150 kg are
  subject to all of the Rules or Articles of the Air Navigation Order.
  As many of these Rules are practically impossible for the model
  operator to meet, the modeller must request a specific written
  Exemption to allow the model to be flown

The CAA homepage for model aircraft is here.

Ah cool thanks :)
But what if its bellow 7 kg, mabie 1 kg? what would the maximum height be?

@user3797758 I've updated my answer, hopefully it's clearer now

@user3797758 For a very light model like that, my guess is that the altitude is limited by how far away you can clearly see it from. Ironically, that means that the smaller your model gets (so the less damage it can do by hitting something), the closer you have to keep it to yourself!


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How can I calculate polar curve?
I recently got the polar curve of an aircraft with the method of Anderson. But this method is too old.
Does someone know a recent method for the polar curve without using CFD?

Did you try Makino-san's method? If you want more precision, you need to invest a lot more work, and the best methods are not necessarily the newest ones.

What do you mean, "too old?" Last I checked, algorithms aren't exactly perishable.

Really? How about Newton?

Here are some other methods (excluding CFD and computational ones) for building up a polar curve:

Wind tunnel testing, one of the earliest methods, still one of the most applied and explored one.
Flight testing ("dynamically scaled" model or a 1:1 real prototype)
Empirical methods (e.g. Hoerner's books on "Lift" and "Drag")
Reverse calculations; i.e. if the performance charts AND the engine deck (force model) is published or known, then the flight performance chapter of the aircraft operations manual could be used, at least to a certain confidence level, to guess about the polar curve for different configurations and conditions.
If you know a few speeds of best endurance/best range glide, you could get an idea of the CL/CD at those speeds, and if you know the mass of the aircraft, the polar curve can be plotted.
Asking the manufacturer certainly could help (if not a model of commercial competition)


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In which countries a medically unfit US pilot can fly?
For example can one get another license in a foreign country?
Which countries allow that?

As long as the medical condition isn't disqualifying in the other country then why not? The US can't tell other countries who they can or can't give a license to. It's hard to say more than that without more information.

of course in many (most?) countries the medical requirements are actually more strict than they are in the US...

It completely depends on the condition. Just because you're denied a FAA medical it doesn't automatically mean you can't get one to operate in another country.
For example, colour-blind pilots can fly up to First Officer level in Australia, and we have no mandatory retirement age. But we are stricter on things like head injuries.

It's possible. One example: Bob Hoover got an Australian license and medical certificate while his US medical was revoked.


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What do Fighter pilots' thumbs look like?
I have to imagine this question doesn't get asked too often, but I read actress Sienna Miller said her "nipples look like fighter pilots' thumbs" from breastfeeding.
I'm so confused. Do pilots' thumbs have a certain way of looking that is known?
I'm a blogger and want to write about her comment, but I'm looking for some context to explain it to our readers with.
Any ideas?
http://www.eonline.com/news/844242/sienna-miller-prefers-her-postpartum-nipples-they-look-like-fighter-pilots-thumbs

I believe the comment is not particular about fighter pilots, rather it is a figure of speech describing the physical changes a female experiences when breast feeding.

I could see that, Kevin, but it does leave me wondering why not just say a thumb in general? How specific the imagery was intrigued me.
Thanks for the reply.

"[Y]ou could hang two wet duffle coats off them with two bottles of Irn-Bru in the pockets." http://rvincent.digital-nerv.net/tag/kate-moss/ http://showstudio.com/project/in_camera/kate_moss (2003)

But perhaps the original thought was related to the 'thumbs-up' that fighter pilots maybe do a lot. "After startup, when the pilot indicates he is ready to go flying, he will pass the thumbs-up to the Plane Captain." https://fightersweep.com/3864/ask-a-fighter-pilot-hand-signals-on-the-flight-deck/ (on an aircraft carrier, but maybe elsewhere too)

I edited your title since I cannot see anything "slightly NSFW" about breastfeeding.  That said, I am European which might make a difference since we see it as totally normal.

That's funny, Simon. I work for a pregnancy/parenting site, so I'm used to an anything-goes, show-all-the-birth-photos kind of environment. Still, I try and be sensitive to other sites that normally don't discuss nipple shapes.
I've not only seen it all, but I've been there and done that (having kids) twice. Nonetheless I wouldn't want someone who's browsing aviation at work to get flagged for looking at a post about nipples and have to report to HR. ;)

Thanks for the suggestions, @Keepthesemind.
(By the way, I don't know if your username is meant to confuse people and make them click to look for what they're supposed to keep in mind, but it got me...twice. Kudos.)

You may want to ask on the English language and usage stack exchange site about the origins of the phrase

In some fighter aircraft there are several functional switches on the control stick--switching from guns to missles and vice-versa, aircraft trim, firing the weapon(s), etc. A fighter pilot's thumb can get a real workout and over time that could result in a very muscular thumb.

Even so, the muscles that actuate the thumb are not in the thumb proper, but in the hand.

Lancer - Just as a nipple can get a real workout, right? Not that I've ever heard of a muscular nipple... That makes some sense all the same, though. Thanks.


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How does a commercial jet descend?
When landing a modern Jet such as the Boeing 737, what is the primary source for descent? The elevators or gravity(from reduced airspeed) or a combination of both? Is the glide path angle of descent a series of step downs where the Jet levels out in steps as its descending? In computer generated simulations , it appears as though the plane stays level throughout the entire descent and I'm wondering if that's actually what happens and if so how it is controlled?

It is a combination of drag and gravity. Both conspire to slow an aircraft down, and it can either add thrust to compensate or descend. Typical descent angles are only a few degrees: Watch the horizon ahead of the aircraft, and you will notice when it descends: The horizon line will slightly move up relative to the longitudinal axis of the aircraft.


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Is it ok to use an iPad (or similar consumer hardware) and electronic charts for GA in Europe?
I'm wondering if it is it ok to use a consumer tablet and electronic charts (e.g. within the AirNav Pro app) instead of the paper version for recreational VFR single-piston flights?
Edit: to clarify, my question is indeed about official, up-to-date charts, accessed with consumer hardware (I mention AirNav Pro, but it could well be any pdf reader for that purpose) as opposed to paper medium.

No, these kind of apps (AirNav, VFRNAV etc.) are not meant to replace paper charts. You'll find phrases like this on most of the websites which offer those apps you will find paragraphs like this:

Please note that this software is not intended to replace a certified navigation device. You should always use official aeronautical documentation when preparing and performing a flight. You should always use certified navigation devices when performing a flight. [Source: https://itunes.apple.com/us/app/air-navigation-pro/id301046057?mt=8 ]

There is certified software like for example Jeppesen Mobile TC available.

I think the important bit for this question is You should always use official aeronautical documentation when preparing and performing a flight. -- so if I loaded (for example) PDFs of a current "official" sectional/IFR chart/approach plate on my iPad, would that be allowed in Europe? (Under the FAA Part 91 rules & AC 91-78 this would be OK...)

You should note that disclaimers like that are in regards to using a portable electronic device + software as a primary navigation system. It says nothing about whether or not approach plates displayed on a tablet are legal for use!

Indeed it doesn't but he asked for software like this and so the answer is no. If you like to know about apps like these from jeppesen or copies of paper charts in pdf form I'm not sure about the legal situation under EASA. I have an 10' tablet with me every flight and there's a bunch of aviation related stuff on it but finally I'm still one who does not go without his own complete and up to date set of aeronautical charts for the whole area. Even if this folder remains on the back seat - I'm 21 and these apps are probably older than my license ;)

@Falk: egid correctly interpreted my question in the sense that the iPad would be just the medium to access up-to-date, official aeronautical data. I will clarify my question to this effect.

@voretaq7; at least in Germany, you're required to carry paper charts, whether you use them or not, you must have them along for the ride.

@roa: do you have a reference for that? could you write an answer?

@roe As abey already mentioned, could you please quote or link to the regulations that require this and add it as an answer to this question?

@PhilippeLeybaert, @abey; I'll try, this is what I've been taught by the local CFIs. IIRC there's the catch with "official charts" and only the paper ones are official, or something like that. A quick google does indeed say nothing about paper (or any other kind of medium)

@PhilippeLeybaert @abey; Also, Germans are notoriously assuming anything technologically advanced will break. And batteries will run out. That's why you can't legally ride a bike in Germany at night with battery-powered lights, you must have a functioning dynamo along. So my guess is, while probably not strictly forbidden to only have digital charts, they're still gonna bust you on the assumption that your GPS will break...

@roe You're not making sense. Either it's allowed or not. You're saying that in Germany it is required to carry paper charts but unless you can back that up with official regulations that's just an opinion of yours. I'm pretty sure it's allowed because Jeppesen's iPad apps have been approved by EASA to be used without paper backup charts.

@PhilippeLeybaert; I'm just relaying what I've been taught. The regulations says nothing about the medium, leaving it open to interpretation. And I've been taught, that that interpretation is paper charts or bust. But sure, as long as it's only "my" opinion and not the one of the guy handing out sanctions, you're fine.


text:
What licenses and/or training should one obtain to be able to fly a drone in California?
The FAA will open up to flying civilian drones in 2015. Should we get pilot licenses to be ready for this? if so, is there a difference between plane or helicopter pilot license?
Links related:
NASA Helps Draw Up Rules for Flying Drones in the U.S
FAA making plans for drone flights in U.S.
U.S. colleges begin offering more drone piloting programs to keep up with domestic drone boom
California bills tackle drones, personal privacy
Aviation schools prepare for boom in demand for drone pilots

I haven't seen anything referencing what would be required, but I suspect no existing license will make any difference unless you intend to fly under that license as well.

Related: http://robotics.stackexchange.com/q/1339/417

Well, I have two answers for you - one personal, and one practical:
Personally, as a pilot (and very occasional airline passenger) I think anyone operating a drone should be required to get a pilot's license of some kind. Maybe I'm just grumpy, but I spent a lot of time cramming the skills and knowledge into my brain that are required to safely operate in the US National Airspace System. It can get pretty complicated and crowded up there, and I think we need the operators of unmanned aircraft to have a thorough understanding of that.
The last thing anyone wants is a UAV smacking into a plane because it wandered somewhere it shouldn't be
PRACTICALLY though, it remains to be seen what regulations the FAA will impose for unmanned civil aircraft - they may require a pilot's certificate (speculating: In the category and class equivalent to the Unmanned Aerial Vehicle you'll be operating), or they may require a "remote operator's certificate" of some kind (perhaps with special emphasis on remote-operation-specific issues like command uplink delay), or they may not impose a requirement at all and treat them like model aircraft until the first accident involving one of these things causes a public outcry.
Like egid said, until the FAA issues a NPRM telling us what they're thinking of doing here we really won't know - your guesses are as good as ours right now.
I would suggest at least an Private Pilot Ground School course while you're gearing up though -- and I would suggest it even if the FAA decides no license is requried for being a UAV operator. The airspace, chart reading, flight planning, and ATC portions of the course are something you'll probably want to be familiar with (and are broadly applicable across all kinds of aviation), and a good ground school course usually isn't that expensive.
(As to whether you take the knowledge test at the end of the course, that's up to you -- the results are good for 2 years in case you decide to pursue a pilot certificate, but the test you have to take as a UAV operator may wind up being different from the one you'd have to take as a private pilot, or may not exist at all, so you might just be setting yourself up for having to take two tests. Again, at this stage your guess would be as good as mine here.)

On the bright side, drone's can't fly in the complicated airspace that you are referring to so it isn't an issue....  Yet....


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What are the requirements for a 'complex' airplane?
Requirements for 'complex' airplane seem to vary between regulators and between pilots, so let's have this settled once and for all.
What is the definition of a 'complex' airplane as defined by FAA and EASA?

For the FAA, a "complex aeroplane" must have:

A retractable gear (not necessary for a seaplane);
In-flight adjustable flaps; and
A controllable pitch propeller.

The FAA's definition is given in 14 CFR 61.1:

Complex airplane means an airplane that has a retractable landing
  gear, flaps, and a controllable pitch propeller, including airplanes
  equipped with an engine control system consisting of a digital
  computer and associated accessories for controlling the engine and
  propeller, such as a full authority digital engine control; or, in the
  case of a seaplane, flaps and a controllable pitch propeller,
  including seaplanes equipped with an engine control system consisting
  of a digital computer and associated accessories for controlling the
  engine and propeller, such as a full authority digital engine control.

However, the EASA has a different definition of a "complex motor-powered aircraft" that is an airplane, which is considerably more "complex":

an aeroplane:

with a maximum certificated take-off mass exceeding 5 700 kg, or
certificated for a maximum passenger seating configuration of more than nineteen, or
certificated for operation with a minimum crew of at least two pilots, or
equipped with (a) turbojet engine(s) or more than one turboprop engine

Note that 5700kg is about 12567 pounds.

Could you add the EASA definition aswell, europeans have a pretty different ideea what a complex is : http://www.caa.co.uk/default.aspx?catid=1799&pagetype=90&pageid=10741


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Can Approach cancel my special VFR clearance if I'm already cleared?
Say I have requested a special VFR to enter Class D airspace. Approach acknowledges and clears me into the Class D airspace. After entering the Class D airspace the airport visibility drops < 1 mile.
Am I required to exit the airspace or can I continue as normal?

Wouldn't it be your job to remain in suitable visibility conditions? I mean, if the visibility is better outside the delta, you need to go there, if it's not, you'd be flying around there illegally as well, so you might as well bite the bullet and declare emergency :)

@roe, Weather, at times, can deteriorate quickly leaving the pilot in less than desirable flight conditions. Declaring an emergency may be the only "proper" way to get back to the airport.

ATC: "N1234 State intentions."

@Lnafziger "yeah, umm, im gonna land right here, would you send a bus please?" :)

@Lnafziger, That is verbatim what ATC said (this scenario has happened to me).

@fbynite I'm not surprised, lol.

Related: When has a pilot legally accepted an IFR clearance?

@Lnafziger: straight from the .65, c. Request the intentions of an arriving aircraft operating within a Class B, Class C, Class D, or Class E surface area.

The clearance comes with the catch that you need to maintain the minimum visibility requirements and sky conditions, if you're not able to, you have no clearance, it's pretty much as simple as that. Either you need to navigate in such a way that you avoid the weather (which might require you to leave the airspace) or you can do one of two things

Request an IFR clearance if you're rated and equipped
Declare an emergency and land in the nearest suitable spot, assuming you can still see the ground

If it is deteriorating so quickly that you cannot go back to where you came from (i.e. the weather is not better outside the D), you'd be flying illegally outside the D as well, so no point in going there really, but more importantly, if the weather is deteriorating that dramatically, you don't have much time before you'll be completely blind, and by that time you'll want to be on the ground with as little injuries as possible, no matter where or the condition of the aircraft.
Note that the minimums are different depending on where you are (jurisdiction) and type of aircraft.

The 7110.65 includes a paragraph on this exact topic. There is a lengthy note, the upshot of which is: The pilot is the authority as to flight visibility; if they deem that FV is less than 1SM they should declare an emergency and ATC should allow them to proceed inbound to land. The note references 14 CFR 91.3 (PIC emergency authority).


text:
Where can I rent a float plane?
Is it possible to rent a float plane with a private pilot's license?
Flying floats is one of the main attractions for me to learn to fly.  However, after some searching on the internet I can only find wheeled aircraft that are available for rent in my area.  Am I missing something?  Are there flying clubs or partnerships that have float planes available?  I would love to fly floats but owning a seaplane is not in the cards for me at this point in my life.

Do you have a float rating? (Upon rereading your question, it sounds like you might be looking for float training. Is that right?)

I do not have a float rating or a private pilots license yet, all I've done is an introductory flight which I really enjoyed!  I want to pursue flying but curious if I can expect the ability to rent float planes once I have all of the proper training.

The Seaplane Pilot's Association publishes a Water Landing Directory that includes seaplane facilities and flight planning maps for cross countries. This lists facilities that offer seaplane rental's. There is a discounted price on the directory for SPA members.


text:
Are TI graphing calculators permitted on the FAA knowledge exams?
I know it's a bit odd, but I like using my TI-89 graphing calculator in addition to an E6B when doing calculations. It helps me avoid dumb arithmetic errors.
I read the section "Use of Test Aids and Materials" of  Recreational Pilot and Private Pilot Knowledge Test Guide (FAA-G_8082-17). It seems to meet all of the requirements except (d), which I don't really understand:

The use of magnetic cards, magnetic tapes, modules, computer chips, or
  any other device upon  which pre-written programs or information
  related to the test can be stored and retrieved is  prohibited.

Does anyone have a definitive answer on whether these types of calculators are permitted?

The document you cite actually goes on to explain what the procedure is for calculators, and when testing centers can prevent you from using your own (you'll be provided a loaner):

Testing centers may provide a calculator to you and/or deny use of your personal calculator based on the following limitations:

a. Prior to, and upon completion of the test, while in the presence of the Unit Member (formerly referred to as proctor), you must actuate the ON/OFF switch and perform any other function that ensures erasure of any data stored in memory circuits.
b. The use of electronic calculators incorporating permanent or continuous type memory circuits without erasure capability is prohibited. The Unit Member may refuse the use of your calculator when unable to determine the calculator’s erasure capability.
[...]

Basically, you can bring a graphing calculator and wipe it, but unless the center is able to confirm that you've removed all stored memory, they're probably just gonna say "nah" and hand you a basic calculator. There's a pretty good chance that your graphing calculator falls under the "permanent or continuous type memory circuits" category anyway.

Haha, I was about to quote the same part along with the excerpt from the intro paragraph just above it that says "All models of aviation-oriented calculators may be used, including
small electronic calculators that perform only arithmetic functions"...  :)

Got it. I guess I can try bringing it, but might get stuck with something else. Thanks!

@Lnafziger yeah, I figured this is the key bit. :)

Yeah, either one answered it so I figured that I would include both.  Not really needed though!

@John As I recall the CATS software has a calculator (four-function add/subtract/multiply/divide) built in and available. You could bring a simple 4-function calculator with you too.

I can actually recommend buying the Casio FX-82 Solar - it is about 10 Dollars and actually the one that is given out for the German ATPL written test. I have been using it ever since, and it has handy features relevant to aviation.


text:
Airplane Strobe Light Pattern?
I saw this question on Google Plus and it seems to be a good question to put here.

Is there a flash pattern for the strobe lights?
  I think I've read that Airbus has ~2 flashes/sec and Boeing has ~1 flash/sec. I've seen both patterns in the air but I didn't know the aircraft type.

It appears that the flash sequences in Airbus and Boeings are different. For example, the following image gives the flashing sequence in Airbus A320:

Image from LED Anticollision Lighting system for A320 by UTC Aerospace Systems
Note the differing flashing sequences of different lights. Also, see this question.
As far as regulations are concerned, 14 CFR 23.1401 - Anticollision light system states that:

(c) Flashing characteristics. The arrangement of the system, that is, the number of light sources, beam width, speed of rotation, and other characteristics, must give an effective flash frequency of not less than 40, nor more than 100, cycles per minute. The effective flash frequency is the frequency at which the airplane's complete anticollision light system is observed from a distance, and applies to each sector of light including any overlaps that exist when the system consists of more than one light source. In overlaps, flash frequencies may exceed 100, but not 180, cycles per minute.


text:
History and results of the GE90 B747 Test
In this article, I read about the B747 testbed for the B777 GE90 engine. Where can I find more information on that airplane?

What do you want to know? Looks like a normal passenger 747 with a different engine mounted on the port inboard pylon. Probably equipped with some additional engine monitoring but not sure its much different than a "stock" 747. In fact, here is a (really short) video of that aircraft/engine combo, and an article.

You may read more in this article:

Boeing 747-121 General Electric Engine Testbed, c/n 19651

As mentioned this is the B747 with construction number 19651.
From this article above:

On March 9,1992 the former Pan Am Boeing 747-121 was registered to
  General Electric Aircraft Engines (GEAE) at the Mojave Airport in
  Mojave, California.
At the Mojave Airport General Electric removed all
  passenger coach seating from the former Pan Am 747 and installed three
  engine data-gathering systems.
General Electric strengthened the
  747-100 airframe to allow it to be capable of flying 747-300 type
  maneuvers, needed for high - inlet - angle, fan - stress and inlet -
  stability testing.
GEAE would attach the test engine to the number two
  engine pylon located on the aircrafts left wing.
(Source: air-and-space.com)

(Source: Airliners.net)


text:
What is the lump on top of the Boeing 737?
What are the lumps (Circled) on top of these two Boeing 737s? I looked it up but I only found the answer for one specific Virgin Blue 737.

Original image source

Also more info about wifi on aircraft

It is the antenna for the inflight wifi system. The Southwest aircraft has a Ku band antenna on the top, allowing it to access the internet through satellites. The United aircraft appears to have a similar system.

It looks like satellite data link antenna discussed here. It provides internet connection for passengers.


text:
Why is New York-London used in time measurement for aircraft?
Looking around aviation news and history, I see that many commercial aircraft are touted to have this or that much time fly between New York and London. What caused the route between these two cities to be used in measuring the "speed" of the aircraft?

As most of the flight is over water, the Concord would be able to fly at supersonic speeds. May as well pick a benchmark that is good for your product. :)

Partly because saving 1hr on the time may let someone do anther days work, due to time zone differences etc.

I'd say it's the same reason we still use "horsepower" as a means of power measurement of car engines.  It has historical significance.

They are (and historically, were even more so) two of the biggest cities in the business world (ranked Alpha++). That specific route has some of the highest rates of business travel and is, therefore, a fairly prestigious, famous route which is popular with fairly wealthy, prestigious people.
They are also two of the most famous cities in the world, and most people know roughly where they are on a map. The fact they're separated by an ocean which is large but was just small enough to be possible to cross safely in the early days of aviation also helped, because it gives the impression of being further than it is.
For example it's a comparable distance to London-Dubai, but that doesn't "feel" as big due to being overland through Europe. Equally while many people know roughly where Dubai is nowadays, it wasn't anywhere near as famous 30-80 years ago.

Also the Atlantic crossing was used to compete in performance between ships since 1830, so that route has tradition long predating aviation (though for ships departure was usually from Liverpool rather than London).

A very good point, Liverpool or Southampton to New York were both used in that way as far as I'm aware.

It's also probably worth noting that, even now, it's one of the busiest long-haul routes in the world, if not the single busiest. Heathrow-JFK is the single busiest route with an endpoint in Europe by passenger volume and that's not even counting traffic between the other airports in NYC and London (i.e. Newark, LaGuardia, Gatwick, London City, etc.) London and NYC aren't really among the most heavily populated cities in the world, but they're both enormous business centers and also huge hubs for trans-Atlantic traffic.

Once a benchmark is set up, it's usually preferable to add data to it and continue using it, than to create a new benchmark, because it permits a comparison between current and previous samples.
So even if the two cities are not the most logical choices now, they were in the past.

I suggest that the particular international air route is used because (1) both countries speak English and (2) English speakers read easily left to right.
I believe that commercial aircraft pilots and air traffic controllers around the world speak English at least as a second language.
The particular route is typically perceived to be longer than many other routes that are the same length yet nearer the equator. Perceptions can be misleading. For instance, on a Mercator projection map, Greenland appears about  the same size as Africa, but actually Africa is 14 times the size of Greenland.

Welcome to Aviation.SE. Please consider supporting your assertions with facts, I suggest and I believe are usually not seen as a great way to answer.

New York to London is a route which benefits from a strong tail wind - it takes 6 hours (British Airways, in a 777) in that direction, but 8 hours from London to New York.

Welcome to Aviation.SE this answer does not really answer my question because I am asking more of why these two cities (Both NY-London and London-NY) are used rather than the specific NY-London route.

Thank you ! (came here by clicking an interesting-looking question in the "Hot questions" column from a programming page).  The jet stream tail wind flatters New York to London flights, in a way that other routes don't.  If round-trip times were given rather than one-way, there'd be less of an incentive to choose those two cities.


text:
Blended wing vs flying wing kitplanes, are there any out there that are in production, horsepower calculations,
There is this interesting plane I like, the horten hx2 and would like to make a 1:20 scale 3d model of this,
but wondered if you doubled an air frames size on such a plane over conventional wing design how much more horsepower would you need
https://en.wikipedia.org/wiki/Horten_Aircraft_HX-2
Crew: 2 Length: 4.5 m (14 ft 9 in) Wingspan: 10 m (32 ft 10 in) Gross weight: 600 kg (1,323 lb) Fuel capacity: 240 L (63 US gal; 53 imp gal) Powerplant: 1 × Rotax 912 iS2 4-cylinder air-cooled horizontally-opposed piston engine, 75 kW (100 hp)
https://robbreport.com/motors/aviation/the-horten-hx-2-flying-wing-launch-2898746/

Welcome Amari!  Here is a link to our community's tour: https://aviation.stackexchange.com/tour

And here is a link to our help site: https://aviation.stackexchange.com/help

We do generally limit posts to a single question, so I'll flag your question as "needs more focus", which will give you an opportunity to edit it.  It may get closed, but that will just be temporary.  You can click on "Reopen" once you've made your edits.

I'll also give you an upvote because it's clear you aren't a spammer, your questions are good, and you may need some rep points to post comments.

A 1:20 scale model of a 10 m flying wing would be close to the venerable Zagi.  RC forums have decades of discussion about this and similar airplanes from other manufacturers.  But briefly, 200 W is more than enough for spirited flying.  Maybe 300 if you add heavy retractable landing gear and a heavy scale canopy to look like the HX-2.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Are fighter jet cabins pressurized?
I heard once that fighter jet cabins are NOT pressurized, but the pilot's suit is, which prevents problems with decompression if the cabin gets shot.
But a military fighter pilot much later told me that the cabin is, in fact, pressurized and that getting shot (the cabin) and the resulting decompression are not that much of a bother, at all.

This answer mentions that they are pressurized, but not as much as a passenger jet.

Historical perspective: Many German fighters of WW II had pressurized cockpits. For example, the models of the Me-109 G ending on an even number had a pressurized cockpit, while the odd-numbered ones had an unpressurized cockpit.

Yes to cool the electronics.

Cabins of fighter jets are in fact pressurized, but not same as the passenger airplanes. Cabin pressure in a passenger airplane will increase (almost in a linear fashion) as the airplane climbs. However, fighters keep ambient air pressure to a certain altitude. It maintains this pressure until a certain pressure differential is met, and then cabin altitude increases to maintain this differential.
Therefore at higher altitudes, cabin pressure in a fighter jet is low enough that supplemental oxygen is required for the pilot(s). This is supplied via On-Board Oxygen Generation Systems.
By not pressurizing the cabin completely reduces stress on air frame and is beneficial during an unplanned decompression.

By the way, your friend (military fighter pilot) is correct.

"Cabin pressure in a passenger airplane will increase (almost in a linear fashion) as the airplane climbs." Surely you meant to say something else. The cabin pressure at cruise altitude is considerably lower than it was a second after the plane took off.

I think you are confusing "cabin altitude" with "cabin pressure" here.

Maybe he meant the pressure differential

@Antzi: Is the F-16 cockpit pressurized? confirms that constant pressure difference is how fighter cabin-pressure systems do usually operate, above a certain altitude, agreeing with other answers on this question.  So that's the right answer, and probably what the author of this answer was thinking but didn't actually type.  (That linked question has good answers.)

Typical Cabin Pressurization Schedule for a Fighter
The A7-E has an air-conditioning systems that maintains the cockpit environment at a specified temperature and pressure. The conditioned air enters the cockpit through a flow control valve and is distributed to vents around the canopy and window areas. The cabin pressure is maintained by a cockpit pressure regulator, which releases air into the nose cone of the aircraft to maintain the specified pressure as detailed in the graph shown below (A7E NATOPS Manual Section I - The Aircraft).
This pressurization schedule has the cockpit unpressurized from sea level to 8,000 feet. Above 8,000 feet, and up to 23,000 feet, the cockpit is kept at 8,000 feet. For any altitude above 23,000 feet a 5 psi differential is maintained between the cockpit pressure and the flight altitude pressure.
The cockpit altitude is displayed on a gauge on the forward console.
The cabin pressurization is regulated when the cabin pressurization switch is in the CABIN PRESS position, and will be dumped in the CABIN DUMP position. Essentially, all air to the air conditioning turbine is shut off. There is also an emergency vent air knob for ventilation, that can also be used to reduce cabin pressure.
Regulations required pilots to be on oxygen from start-up to shut-down.
Managing Oxygen & Pressurization
I volunteered to go ashore in Greece to be a liaison between NATO forces there and the USS Nimitz. They were concerned about US aircraft entering Greece airspace to conduct their scheduled missions, while Turkish fighters were also violating the same airspace. I was to be ferried in an S3.
I was in the back seat in the TACCO (tactical officer) position on the right-hand side. We had taken the catapult shot and were climbing out. I was talking with the crew member across from me in the SENSO (sensor operator) seat when he asked me how I felt. "Dizzy," I said. He pinched a fingernail and told me he was going to checkout the pilot and copilot. He came back and said they had lost cabin pressurization, and that we needed to put on our oxygen masks. I had been flying for so many years with the oxygen mask always strapped to my face that I never paid attention to the signs of hypoxia. It always amazed me all the various ways one could get in trouble airborne.

Yes they are. There are two pressures available to aircrew of fighters. One is a combat pressure for minimizing decompression if the cockpit is hit. The second is for ferry flights where a more comfortable pressure is maintained to reduce crew fatigue.

Pressurisation is required in fighter pilot because as per altitude increase pressure reduces so it is required to maintain the cabin pressure relative to ambient pressure...

welcome to aviation.se. I'm sorry, but I don't fully understand what you mean with as per altitude increase pressure reduces so it is required to maintain the cabin pressure relative to ambient pressure, could you please consider writing a more complete answer?


text:
Can self-study and FSX substitute for the majority of PPL training?
I am 16 and am very interested in becoming a private pilot, and fly flight simulators. I do not have enough money for the entire training. I can only afford 5 flying lessons.
Is it possible to learn majority of flight maneuvers using a flight simulator and just take a few lessons to get used to the feel of a real aircraft?
What are the list of topics that you need to learn when gaining your private pilot license?

Which country? UK? Anyway, the answer will be: no

Related question: Can Microsoft Flight Simulator help me learn to fly (or make me a better pilot)?

I would say if you are good at what are you doing you can pass any test first time. So,answer is yes.

Since you need a minimum of 45 hours (in the UK at least), then no, it is not possible.

@vasin1987 - but a student won't even be allowed to attempt the checkride without the prerequisite amount of flight time. Please post your comment as an answer so i can downvote it :)

@SteveV. Of course all the prerequisite must be met no matter how many times a person take a test in order to pass it. He needs the require flight hour and all classes but if he is good he can pass all on the first attempt. And for post as answer, i recline to do so :)

No! Stop! The simulator I did before taking actual flight lessons was useful only for learning bad habits.

There are usually a minimum required hours of flying you need to do, so the answer is no. Simon mentions in the comments that in the UK the minimum hours is 45.
If money is of issue, you should also consider other options such as gliding which is considerably cheaper. At least in Finland if you gather enough hours in a glider, you can then get other licenses with less hours required. Besides after getting enough hours you would be older and perhaps have a job that can pay for our hobby.

Unfortunately, no.
If you learn and practice and master the flying skills in a flight simulator, you will become a certified pilot only for that simulator, not for real life.
You didn't mention the country, but you can look at this answer to find all the requirements to become a private pilot in USA.
Using a flight simulator, you can learn many very valuable skills which will be very useful in your actual flying (and many many pilots do a lot of practice in a simulator), but in no way it can completely replace actual flying. There are many things you can only feel in actual flying experience. You can make any mistake in a simulator and no harm is done, but not in actual flying.
Everything in flying is expensive. Even after you get your PPL, you still have to pay for flying afterwards. Since you are young enough not to have chosen a career path yet (probably), why don't you try to become an airline pilot?
For the answer to your second question, a few topics are:

the airplane and its physics
its engine
weather
effects of weather and altitude on pilots
navigation
planning
... and many other topics

There are tons of material available covering these topics. FAA has a wide array of reading material which you can download for free.

You forgot the largest topic of them all; rules and regulations. :p

@falstro Oh yeah, that's true. But I thought OP was seriously looking to learn flying. ;)


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What happens if fuel tanks are hit by gunfire?
In June 2014, a PIA airplane was targeted by machine gun fire while landing.
I wonder what would had happened if the fuel tanks were hit? An explosion, perhaps?
But in an episode of Myth Busters, they did shot at a gasoline tank and found out it didn't explode. No ignition temperature was reached they said.
So, what would be the worst case scenario if a bullet hits the fuel tank on an airplane?

diesel and jet fuel is very similar, so I expect very little from just gun fire,

Related: How does a fuel tank fire self-extinguish in an A380?

The worst case depends on the kind of bullet. If a tracer bullet hits an empty fuel tank which contains a mixture of air and fuel vapor, an explosion will follow. A regular bullet will just punch a hole into the tank, but will not be hot enough to start combustion.
On today's airliners and combat aircraft the fuel tanks will be filled with an inert gas, so there is not enough oxidizer present to support combustion. Even the tracer bullet will have no effect. Now the tank will have a hole, however, and if it is below the fuel level, some of it will leak out and could be ignited by a hot object. This will be the main source of fire, but will not lead to an explosion.
Since WWII, most military aircraft used self-sealing tanks, to much the same effect. This was a double-skinned tank with a rubber middle layer which would swell when wetted with fuel and close the hole.

military aircraft still use self sealing tanks

@ratchetfreak: Right, I corrected the sentence.

Where does the inert gas come from? Onboard Tanks? Argon?

Argon is a rare noble gas, and hence very expensive. The cheapest available gas is nitrogen. AFAIK military aircrafts have bottles of compressed nitrogen with them. However, e.g. a A380 carries ~300,000l of fuel, a big gas bottle contains about 30,000l. So you need 10 bottles for each long trip, being refilled after... Instead, they generate the inert gas during the flight. They use a membrane allowing nitrogen atoms to pass more easily than oxygen, resulting in a gas with only about 12% oxygen. This is low enough to prevent an explosion in the tank.

By the way, during WW I, Germany sent hydrogen airships to England. England first tried to shoot them with standard bullets, but this did not ignite the hydrogen. And the small holes did not affect the airships. The trick was to use tracer bullets with phosphor which could ignite the gas streaming out of the airships punched by regular bullets.

@sweber you have enough additional information in your comments to create your own answer....

the key word with tracers is 'could'  In the episode of mythbusters referenced, they showed that it isn't a given (it took a number of tracer rounds to get the result they wanted) @sweber Hydrogen ignites a lot more easilly than petrol, petrol more than diesel, and diesel more than jet fuel.

@sweber: Argon is not "rare" - the earth's atmosphere is 1% argon!

OK, let me expand my comments about inert gas to Peter Kämpf's answer to an own answer.
Argon or Nitrogen ?
It was asked if Argon is a suitable inert gas. While in principle it is, it is also a rare element and so expensive. A better choice is nitrogen. It makes up 79% of the air and is much cheaper.
For example, I found ~50€ for a 50l bottle of nitrogen and ~100€ for argon.
But one also has to keep in mind that the production capacity for argon is not very high, so if aviation starts to buy large amounts to use it as inert gas, the price would increase soon.
Argon and nitrogen are gases which can not be liquefied at normal temperatures, so they are stored under pressure in bottles like this:

They are made of steel to  withstand the pressure of up to 200-300 bar (atmospheres). So, a big 50l bottle has a weight of 77kg without filling (sorry, german).
Nowadays, also civilian aircraft are often equipped with an inert gas system, since the central wing tank of TWA800 exploded most likely due to electrical short circuits
But when it comes to larger aircrafts with larger tanks, gas bottles become a problem: The A380 has a fuel capacity of 325,000 liters. Imagine you want to fill its tanks from the 50l bottles mentioned above. The content of one bottle expands to 10,000-15,000 liters at sea level pressure, so you need 20-32 bottles for the A380.
This bottles have a weight of almost 2.5 tons and need some space. The high pressure is also an issue, and of course, you have to refill the bottles after each flight.
So, it's not a good idea to use this system on larger aircrafts.
I was quite sure that I once read that at least small aircrafts like fighters use bottles, but I don't find any evidence. On the other side, a F35 can carry up to 10,000l in its internal tank, so it would also need a 50l bottle. So, I think I misunderstood something.
CO2 ?
The benefit of CO2 is that it becomes liquid under pressure, You won't need so many bottles and the bottles themselves would be lighter. But CO2 may act corrosive if it finds some drops of water, as it turns to carbonic acid.
Exhaust gas?
A gas that is the product of a fire doesn't burn any more.
This is indeed used to fill the tank of large ships, but you can not take it from the main engine: Those are diesel engines always working with an excess of air, so the exhaust gas contains oxygen. The ships burn some fuel with a balanced amount of air in a inert gas generator.
As fans are similar to diesel engines in this context, exhaust gas is no solution. The gas also contains CO2 and water, so may be no good idea in general for aviation.
Halon
Many older combat aircrafts like the F16 use halon to extinguish fire, but also to fill the tanks.
As halon is one of the worst greenhouse gases, its production has been abandoned 1994 and this document describes the search for alternatives working largely the same way:
To explain it in short: Inside a fire, molecules of the burning material break up and connect to oxygen atoms. This connection is what gives the energy we want in our engines and we want not in the tank.
Halon jumps into the reaction and connects itself to the open ends. The reaction between oxygen and the material, which gives the energy, can not take place any more.
It is said that about 6% of halon in air is enough to extinguish fire, 10% and more can be survived, if exposure time is not too long.
Halon was not used as inert gas, but it was injected into the tanks shortly before a fight was expected
On-Board Inert Gas Generation System(OBIGGS)
Today's solution is to use a On-Board Inert Gas Generation System(OBIGGS) developed by NASA/Boeing
It uses some kind of membrane which can be passed by nitrogen more easily than by oxygen. Bleed air is lead to this membrane with some pressure. The oxygen is kept back and you get air with a significantly smaller fraction of oxygen behind the membrane. There are devices on the marked which produce 2lb/min with up to 1% remaining oxygen
The goal is to have not more than 9-12% in the tank, see the link to NASA above.

By the way: In WW I, Germany sent hydrogen filled airships to England. One could guess just shooting at them would take them down, but the holes were too small to cause a reasonable loss of hydrogen. And unless the bullets made sparks when hitting some steel in the ships, they also did not set the ships on fire. It turned out that firing standard munition at airships was quite useless.
The solution was to use phosphor based tracker munition which set the hydrogen streaming out of the leaks from the other bullets on fire.

A reference or two would make this a spectacular answer!

Combat aircraft like the F-22 have an onboard oxygen generation system (OBOGS) which generates oxygen-enrichded air for the life support system. They don't need bottles, the just feed the off gas from the OBOGS into the fuel tanks.

That's true. On the one side, you get O2 enriched air, on the other, you get O2 degraded air. In contrast to combat aircrafts, I guess the enriched air is not used on civilian airliners.

I often feel like they pipe oxygen degraded air into the main cabin on transpacific flights... :-)

By the way: Zeppelin Luftschiffbau made sure they did not use any sparking materials in the Zeppelins. Bullets simply could not produce sparks! If you look at what they did for spark prevention, modern designers could still learn a lot from those people! Would be worthy of a question of it's own here ...

I read somewhere years ago (Setright 'The Power to Fly'?) that some German WW2 combat aircraft had the fuel tanks vented to an engine exhaust port, via a capillary that cooled the gases and presumably prevented the possibility of flame propagation (in the event of some air being present) in the manner of a miner's lamp. I would guess this would need something to prevent the tube icing and of condensation in the fuel - a hygroscopic canister? Also a one-way automatic suction-relief bypass valve to the atmosphere in case of blockage? I remembered it after TWA 800.

@PeterKämpf no, they don't. Some aircraft do that, fighters tend not to use that method.


text:
What flight and route information do pilots need for flight?
A pilot needs some information before and during flight like METAR, TAF, NOTAM's, Charts, Frequencies, and so on. I want to build someday ,when I have enough time, a website, for private use (Flight Simulation), and maybe when I get the project to work good for public too, that displays all of that data. One should be able to input Departure and Arrival Airport and then get displayed all the Information named above about those two airports. The real question:
What do pilots still need except the above named? Have I forgot something. What would you implement, what would you like to have that makes your pilot (real or flight sim) life easier? Do you know a nice option in the GARMIN G1000 that could be implemented. But please only possible things. An artificial horizon is nice and would be even possible more or less but is very hard to program and is useless for flight simulation.

There are many flight simulator pre-flight briefing programs already. Maybe have a look at them for inspiration? This one comes to mind: http://www.flightsimsoft.com/pfpx/ As for an artificial horizon, I don't understand what you mean. How would that have anything to do in a pre-flight planning/briefing?

Thank you, because of the artificial horizon: I also want to provide some in  flight information. But I just wanted to say that a AH wouldnt be possible.

Welcome Noah! As it is, the question seems too broad for complete answers, and might be closed for that. You may want to read questions tagged flight-planning and try to edit your question to reduce the scope.

@mins I think my question is like a discussion or brainstorming question. Is there any way to mark it as such or something else?

Actually no, and that type of discussion is not the regular way this Q&A site works. You can read more about that in the help center. However, there is a chat tool which can be used for discussions and brainstorming.

You might want to read some aviation textbook about flight planning. It takes at least an entire chapter, and that's just for VFR flight planning. After that you have IFR flight plans, ETOPS planning etc. etc. So in short, this question is way too board to be answered on the site.

I might be able to help a little, I am a professional software developer and also a recreational pilot in Australia.
Starting firstly with the requirements for such a site.  Data for different countries is often sourced from different locations, so you would need to investigate that.  I can only speak for Australia, but we have a web service that we can log into which provides us with weather briefings (METARs, SPECIs and TAFs, as well as ATIS for some Class C airports) and NOTAMs, and which also allows us to submit flight plans.  There are a few apps available which link in with this system, and you could definitely get yours to do the same.
Charts are again something that will differ between regions, and you will need to source these.
On to flight planning itself, you've mentioned the basic things you need.  I only file VFR flight plans, so I can only speak for those.  I start by finding my origin and destination on my charts and ensuring I have all the charts required for the flight, and that they are all up to date.  I have a look for any PRDs (prohibited, restricted or danger airspace) along a direct route, and plan around them by selecting waypoints that will take me on a track away from them.  I avoid controlled airspace where possible and look for major landmarks that I can use as visual cues along the way.  If your system could tell me straight away what PRDs I'll be breaching, whether they are active (from the NOTAMs), and if so, plot a course away from them, that would probably make it stand out from the crowd.
Once I have my route, I look at the LSALT (lowest safe altitude) along it (by looking at the terrain elevation and any obstacles), and work out my cruising altitude, conforming to the hemispherical level rule (odd altitude for track 000-179, even altitude for 180-359, plus 500 feet for VFR).  Again, your system could look at the terrain in the area and suggest an altitude for me which conforms with this rule.
Once I have my exact route (both horizontal route and vertical route), I work out my TOD and TOC (top of descent and climb), mark those on the charts, and then work out my fuel burn by looking at the forecast winds at each level and calculating how much head/tail wind I will have, plus any offset I need to counteract any crosswinds (which may affect my groundspeed if the offset is large enough).  There are a few apps out there now that will do this all for you, so I would expect you would want your system to do the same.  If you're serious about this project, I would recommend getting your hands on a wizz wheel and learning how to use that.  That'll give you a good idea about how the calculations work, and you should be able to make a few algorithms from that.
To give you an idea, below is my flightplan from a few days ago:

Then it's a matter of filing the flight plan and going for a fly.

Wow, thank you, very good Information. Sorry for the late comment, somehow your answer didn't show up in my inbox.


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How to find waypoint IDs?
Is there a website to find waypoint ID's from coordinate values?
I am looking for waypoints in the Indian ocean area.

One possible source is Skyvector

You can use it like a paper map using the Latitude and Longitude markings to find waypoints (or other positions).
E.g. What waypoints and routes are near S30°0.00' E112°00.00'

Hints: Click "World Hi", use your mouse's scroll-wheel to zoom, play with "Layers".

There are also sites with lists, by region, of waypoints with coordinates. One example is fallingrain


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What is the purpose of the sharp pods under airliner wings?
What are the pods with the sharp trailing edges underneath the wings of large airliners, as shown in the image below?

My best guess would be fuel tanks

FWIW, most airplanes use the entire wing as fuel tanks. The inside of the wings. They look deceptively like there's not much space in there but wings are one of the largest structures on an aircraft and they're actually very thick when designed for good aerodynamic efficiency and are therefore the largest bit of unused space. The plane in that picture specifically has fuel tanks in its wings (and maybe horizontal stabilizer/tail).

Thanks @slebrtman! I knew that the main tanks were in the wings though, thought it might be extra tanks (-:

They are called anti-shock bodies and they let the flaps go down and out at the same time. Inside them there are many levers and arms that let the flap do this.

NOTE: whatever the chosen and most upvoted answer says,  THEY ARE NOT ANTI-SHOCK BODIES nor fuel tanks. They are fairings of the flap mechanism.

They are Anti-shock bodies.
In the transsonic speed range (above about Mach 0.7), aircraft drag is governed by Whitcomb area rule, which basically says that to minimize drag, the aircraft cross-sectional area must change as smoothly as possible, independent of its actual shape. It is somewhat counter-intuitive, but well established.
Compare this Junkers patent drawing (via Wikipedia):

which shows various combinations of positioning engines to adopt the area rule.
For the usual aircraft design the cross-section increases over the engines that hang ahead of the wing leading edge and then the thick part of the wing and wing box (the thicker part of fuselage where wings connect), but the wing tips are too thin and the cross-sectional area would decrease too quickly, so something needs to be attached to the trailing edge to make the reduction of cross-sectional area smoother. The anti-shock bodies are usually conveniently combined with flap actuator and track fairings.
There are however some aircraft that have anti-shock bodies combined with other functions, e.g. Tu-134 (and many other designs by Tupolev Design Bureau) retracts landing gear in its anti-shock bodies (which are just one large on each side):

The flap actuator and track fairings exist on all aircraft that have flaps that extend aft as well as down (Fowler flaps and their double-slotted variants), but on slower planes they are much thinner. Compare e.g. ATR-72, which does not need to be area-ruled with its maximum Mach 0.55.

The flap mechanism of the ATR is also much simpler and would not benefit from long fairings. The flaps rotate around a hinge point located far below the wing whereas the Fowler-type flaps move back along rails which extend beyond the training edge when the flap is retracted. Due to the lower speed, the flaps of turboprops need not to be as complex as those on jets.

Albeit being technically a very good answer, it is unfortunately formally not correct because that features in the picture are just fairings for the flaps tracks and they have nothing to do with antishock bodies if not, if any, as a byproduct.

At least for Boeing aircraft they are solely designed as flap track fairings. Very nice answer but unfortunately not really fitting.

Wrong!  They are just aerodynamic covers for the mechanical actuators and mechanisms to extend and retract the flaps.

@CharlesBretana You can't just add "This answer is just WRONG." to someone else's answer (even if you're right). If you think an answer is wrong, downvote it and leave a comment (as you've done). Also, see our Meta discussion on the topic.

@Bianfable, Sorry, didn't know about the rule. I will delete my trailing comment in the ops answer text. Oh I see you already have! Thanks.

Adding to the substance of this answer, Military jets designed in the 60s and 70s used a principle called https://en.m.wikipedia.org/wiki/Area_rule, but these under wing fairings are just flap actuators.

They are not fuel tanks, the fuel tanks are inside the wings.
Those are covers for the flaps actuators: since the actuators and their rails protrude beneath the wing, without a cover they would greatly increase drag. The covers are more aerodynamic and thus produce overall less drag (at the expense of a slight increase in overall weight)

They are not anti-shock bodies nor fuel tanks.

The A320's flight manual (see slide 24) calls them "flap track fairing" since they are... well, fairings for the flap tracks and those fairings are just as big as needed to smoothly cover the flap tracks, nothing more nothing less.
The following picture (my work) shows one of these tracks of an A300 with fairing removed:

The straight yellow part (which I underlined in blue) is basically a rail fixed to the wing on which the two flanges (circled in green) slide toward the left bringing along the flaps; an endless screw (in red) actuates the sliding. The shape of the fairing can be understood from the background of the assembly: as visible, it is just as big as needed to enclose the structures, nothing more, nothing less.
So they don't carry out the duty of anti-shock bodies (or any other aerodynamic function) if not as a byproduct. Anti-shock bodies used to look like a bulge behind the trailing edge and aligned with the chord and protruding both over and under the wing, like in the Convair 990:

In modern jetliners that function is taken over by the quite big fairing located where the wing meets with the fuselage, in yellow on this A380 picture from Wikipedia:

Luckily enough these two pictures were taken from more or less the same angle and this makes the comparison easier.

There is a lot of misinformation here, and the top answer tries to combine concepts from two different applications. These 'pods' are flap track fairings, sometimes called trailing edge fairings, and their purpose is to cover and reduce drag over the heavy duty mechanisms that extend the flaps of an aircraft wing during high-lift operating regimes. See https://en.m.wikipedia.org/wiki/Aircraft_fairing
These pods are not anti-shock bodies, despite nearly all answers trying to use it as a buzzword. Anti-shock bodies are attached to the upper surface of the trailing edge (unlike flap track fairings, which are attached to the underside). Anti-shock bodies were used to reduce the shock that occurrs over the wing while traveling at transonic speeds. They were made obsolete with the advent of supercritical airfoils, and no longer found on modern aircrafts.

Welcome to the site, AJ Zhang! They are indeed fairings but made larger than necessary in order to smoothen the cross section area distribution over length. So they indeed serve both purposes equally. Supercritical airfoils need them as much as the old-fashioned sort did.

But are they formed such to affect the area rule of the whole aircraft as the current "winning" answer suggests @PeterKämpf

@Jpe61 … and at transsonic speed their Y and Z location is less important - what counts is the distribution of the total cross section over length. No "but" necessary.

Is there a definitive source that states they are equally performing the function of area ruling? @peterkämpf saying so does sorta list as a definitive source, but other than that, with all due respect? I find it odd that to offset the adverse effect of engine pods, these fairings would be necessary tens (?) of meters away from the engines.

@Jpe61 In this answer I use a picture from VC-10 development showing their effect at Mach 0.9. Unfortunately, the dumbing down of NASA pages has deleted the original sources (like http://oea.larc.nasa.gov/PAIS/Concept2Reality/area_rule.html) where this picture appeared online first. And Küchemann bodies do not "offset the effect of engine pods" but offset the sudden drop in wing thickness due to rear loading.

@peterkämpf for me seeing is believing, and now I have seen. Thank you!


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Where to find a waypoints/fixed points, navaids and airports database?
I wonder if it is possible to download a database with waypoints, navaids, airports and airways between them. I've been working with AIP documents but it's difficult to get raw information from them and they only have information about waypoints.
I happened to find skyvector.com and I thought there would be an easier way to obtain that amount of information.

navigation charts, which you would find on the site of the local aviation authority. You'll need a current set for IFR flight.

People around X-Plane maintain the data originally from NIMA and DAFIF that were discontinued because some of the authorities stopped providing the data publicly. Quality varies depending on where public data are available from official authority and where not. Not appropriate for actual aerial navigation, but it covers whole world and is easily machine-processable.

Try navigraph.com or NavData from AeroSoft. They provide data for flightsimming, but the data is quite accurate.

@SentryRaven  Very good data, and up to date (at least by a few weeks or so) but is a subscription service.

@Simon Correct. The questions was where, free was not a requirement :)

@SentryRaven  The comment was more to the OP, I should not have tagged you.  Cheers

Jan Hudec, thanks for the X-Plane link. That looks like an excellent resource. Further info: documentation is at http://data.x-plane.com/file_specs/XP%20NAV810%20Spec.pdf

Nice question. There are several ways how to get these information.

http://www.fallingrain.com/: free to use, no registration needed. World database of the airports and waypoints. From these information you could easily make DB for waypoints.
EUROCONTROL EAD (https://www.ead.eurocontrol.int/eadcms/eadsite/index.php.html): free to use, registration needed. Big advantage - real and up to date information for all ECTL countries. But a bit difficult navigation.
JeppView (http://ww1.jeppesen.com/): very expensive SW, but the best in this time. You will find there all information which pilot needs. But it is not real database.
Garmin for pilots (http://www.garmin.com/en-US/explore/intheair/): another not free SW, very similair to JeppView but lightweighted.
NAVIGRAPH (http://www.navigraph.com): Great DB of all things which you need in FMC. But I guess that they have it just for flight simulator.
OpenFlights (http://openflights.org/data.html): free DB of airports, airlines and routes. You could downlod all data in one file :-)

I use the National Flight Data Center at http://nfdc.faa.gov
I had to write them a letter explaining why I wanted the data (http://fplan.sf.net) and they provided me with a login.
Now, every 56 days, they send me an email telling me there's an update available.
Bad news: they recently switched from a flat file to some unbelievably convoluted xml format that I haven't yet written a parser for.
Also, it comes with a disclaimer that the data is not approved for navigation. Given that I've already found two minor errors in it, just in the SF Bay area, that's understandable.
Edit: I forgot to mention that I keep a subset of the data on-line at SourceForge. I try to keep it up to date. It's at the Fplan project. These files are in the old "nav" format; documentation is included in the zip file.
If someone needs these files, they're freely available and I'm happy to make small additions to the data if anybody wants, since I already have the tools to parse the FAA data files. I'm also happy to share the tools if anybody wants.

Good news: I checked back and the old "legacy" flat files are still available for most of the databases. I don't know how long that will last, but for now it's good.

Haven't registered yet but does this only contain US data?

Yes; I have no idea where you would get data for other countries. I expect that each country has its own database, and no idea if it's publicly available.

Another good one for airports and navaids: http://opennav.com/ - has VORs, waypoints, etc.

I have successfully used The GPX Aviation Waypoint Generator from the free Navaid database (http://navaid.com/GPX/) that outputs a GPX (XML type) file with all the waypoints, airports and every other elements you choose to include.
To make a request on this API, make sure you specify the min and max GPS coordinates of the area you want to cover. This is a world wide database, not only for the US.

This is my first post so bare with me.  I don't know if you are trying to get one region only or a global data set.  The issue is that member states are responsible for their own airspace and thus airport/NAVAID/intersection/waypoint/so-on-and-so-forth location data.
You may want to see about getting a copy of ICAO document 7910 "Manual of ICAO identifiers"  This book cost money though.
If you are interested in the North American region (U.S./Mexico/Canada/Caribbean/and-so-on) then you can get for free the FAA Location Identifier book with FAA Order JO 7350.9x.  The lat/long of every waypoint/NAVAID/Airport and the like is in it.  Unlike a previous answer post you don't have to ask for access permission either.  To keep things simple here is a link.
FAA Location Identifiers
 That's what I got for you

Updating: The link is at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/NASR_Subscription/
This provide the text file along with layout data for all the fixes, etc.  The CIFP can be downloaded as well, but the layout is commercialized (~$400).  I have not been able to programmatically download the zip file.

Seems to only cover the USA.

It's unclear what you're trying to update here. If you want to update an existing answer, please do it by editing it, not by posting a new answer.

Only because I had <10 reputation, and it's been a few years since an answer was posted, did I enter a new answer.  I am updating the link to the FAA text database, which would fully answer the question because all the requested data is at that URL.

After some time spent to compare multiple open source data providers, I came across OurAirports.com - which includes worldwide airports, navaids, & frequencies.  This is my favourite source thus far (with new updates going into September 2021):
I was in search of an airports database with good (well populated) records of especially smaller strips/airports across southern Africa. I came across this open and shareable .csv datasource and found it well populated and accurate thus far (if it includes most small dirt strips in Mozambique - I'm sure the rest of the world
s coverage must be OK ;) ). It includes other relational datasets and unique ID's for all airports - so useful for creating a database with future update functionality from the same source.

Is this a product that you are affiliated with?

@KorvinStarmast - No I am not affiliated with this in any way


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How to programmatically access AIP data, METAR, TAF, NOTAMs?
I'm looking at developing an app where one of the functions I would like to implement needs to use data which is normally available in AIP, like:

Aerodrome names, ICAO codes, GPS location, elevation
VFR reporting point names, GPS location
Nav points (names, locations)

In addition, I may want to display or use data from NOTAMs, METARs, TAFs, etc in my app.
Does anyone know the official sources for this data, ideally published by CAAs (FAA in the US, Eurocontrol in the EU and similar)? Please note I'm really only interested in programmatic access (e.g. a JSON, XML or similar feed available through a web API or similar), as opposed to document based data in the form of PDF or HTML files.
It goes without saying that I would ideally like this access for free, but a commercial arrangement is also I would look at - provided it's not outrageously expensive.

Related: Where to find a waypoints/fixed points, navaids and airports database?

I have had a look at that post, but majority of the information there lists either the AIP documents (which are PDF or HTML and therefore not really suitable for programmatic access) or non-official sites, primarily aimed at sim communities - unless I missed something.

ICAO is offering a very nice API for retrieval of, for example, aerodrome names/ICAO codes and NOTAM's. It is currently in public beta, which means that it is free to use. Once they finish testing it, there will be some kind of cost involved, but they have not published any pricing details yet. You can find it here: https://www.icao.int/safety/iStars/Pages/API-Data-Service.aspx
NOAA offers API access to weather information such as METAR's and TAF's: https://aviationweather.gov/adds/dataserver
You can find waypoints and navaids, including names and locations, via EUROCONTROL EAD: https://eadbasic.ead-it.com/fwf-eadbasic/restricted/reporting/reporting.faces (register first, then return to that link). However, what they seem to offer is a one time search/database dump, more than an actual API.

Thanks! I'll have a proper look at the links above this evening, but it seems like most of what I need if not all is there.

You can find a nice set of APIs at:
https://developer.laminardata.aero/documentation/notamdata/v2

Thanks a lot, I'll try it out!

Recent update to aviationweather.gov puts the metar here: https://aviationweather.gov/data/metar/
Raw format for example returns
KRNT 071833Z 19006KT 10SM FEW023 BKN031 OVC037 11/08 A3006 RMK AO2 T01110078


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Is there a legal maximum altitude?
In the US, is there a highest legal altitude allowed for certain planes and does it depend on the plane? I heard from a sort-of-reliable source that the maximum is 45,000 feet but I haven't been able to confirm this. I ask since a plane I travelled in very recently was travelling at an altitude of over 55,000 feet and, when it did, turbulence was terrible (some told me I was lucky to be alive).
Note: I have tried Googling this and have found no answers.

Each plane has it's own maximum altitude at which it's safe and able to fly. Some are very very high - the U2 can go up to 75,000 feet

Just curious, which plane were you in?

@Jon Emirates EK237.

It's almost certain that you were not flying at 55,000 ft. That's 12,000 ft. higher than the aircraft that is used to operate that flight (a Boeing 777) is certified for. It seems unlikely that it would even climb that high if they tried to get it up there.

@reirab Well, I wouldn't gain anything by lying. I had my eye on the altitude and it kept hovering between 53,000 ft and 55,000 ft for about 1 hour. So ...

Strange. Technically speaking, the service ceiling is defined in terms of pressure altitude, so I suppose the absolute (MSL) altitude could go above that value in the right atmospheric conditions. Perhaps that's what happened.

@AhaanS.Rungta Where exactly were you reading this information?

The screen in front of me.

It looks like EK237 is a Boeing 777-300ER (twin-jet) (B77W).  Service ceiling from wikipedia claims to be 43,100 ft.

Yep, just as @reirab said.

@reirab while the pressure and absolute altitude can vary, it doesn't vary by 10-12,000 ft even if we assume the plane was at its service ceiling

@JonStory Agreed. This is what made me wonder where the data feeding the IFE systems actually comes from, prompting this question.

Well above the altitude capable of any current air breathing aircraft you eventually brush up against space which does require certain clearances/notifications to the FAA to enter.

@Dave: But it is quite legal to ascend to altitudes that are (by definition) space, given those required clearances.  For example, the Spaceship One (which is by any reasonable definition an aircraft) climbe to altitudes above 100 km.

@jamesqf correct, however 100km is right at the karmen line where may say space begins. The FAA does not actually offer a hard line for space which makes this whole thing ever more complicated.

@AhaanS.Rungta just in case it wasn't clear from previous comments - it's far more likely that the IFE was malfunctioning than it is that you were travelling at that altitude. It's unlikely the aircraft would even attain that altitude if the pilots tried (and for them to try would almost certainly result in them losing their jobs).

related: Is there a height limit to national airspace?

There's no legal limit of how high you're allowed to fly by law: there's no law that says

It is illegal to fly above X,000ft

In some juristictions there are more specific laws, eg

It is illegal to operate an unpressurised aircraft above 25,000ft

However, each aircraft has a service ceiling when it is certified, and it would be generally illegal to operate the aircraft above this altitude (because it's unsafe).
I'm fairly confident that you weren't at 55,000ft. No currently-operating commercial airliner I know of has a service ceiling higher than 45,000ft (the newer -800 version of the 747) and they almost never operate above 41,000ft. A few private jets can go a little higher, up to around 50,000ft, but I know of no non-military/experimental aircraft which is currently capable of going much above 50,000ft, even if you were daft enough to try.

There are actually a number of private jets certified to 51,000 feet....

"Around 50,000ft" - near enough for the purposes of this answer, and either way none I know of hit close to 55,000ft

If the service ceiling is in the LIMITATIONS section, then it's a hard limit like Vne. If it's in the performance section, then it's information. And not a limitation. 91.13 applies. See this accident report http://en.m.wikipedia.org/wiki/Pinnacle_Airlines_Flight_3701

That report has nothing to do with the service ceiling as compared to performance ratings. There is only one limit for each aircraft and that's the one it's illegal to exceed, other performance figures are hardly relevant to this question.

@Lnafziger, wouldn't that be the physical limit of the jet rather than the legal limit that the poster was enquiring about?  (kinda like there's no max speed limit on the Autobahn. the limit is the physical limit of the car?)

The Concorde actually had a service ceiling of 60,000 ft, but, as far as I know, you're right that no current airliners are anywhere near that. EK237 is operated by a B777, which has a service ceiling of 43,100 ft.

@AngelKoh No, if an aircraft is certified to 51,000 ft. (as several that I have flown are, such as the Bombardier Learjet 31A), then it has been demonstrated that it can actually fly there and it is legal to fly there.  In some conditions, it may be possible to exceed that altitude, but it is not legal because it was not certified to do so.

@reirab true, but unless there's been a lot of work done on the refurb Concorde in the last few week, none of them have been airworthy for a while :)

@JonStory Yes, that's why I said you're correct that no current airliners are anywhere near that. :)

Jon Story's answer is correct, but I will add that the cabin displays often have incorrect information on them. I have seen wrong times, wrong locations, impossible flight paths, impossible air speeds, etc. The mere fact they call it an "entertainment system" tells you something.
I suspect the altitude may be coming from a cheap, dedicated GPS unit. A lot of GPSs have inaccurate altitudes. Some have a "barometric" sensor-derived altitude which is often wildly incorrect.

The max allowed altitude has little to do with jet ability climb over 50k feet. The regulation that determines it is simple: it must be 4 minutes or less it takes the jet to get to 14k feet safely in the event of sudden decompression. Private jets are usually capable of doing that such as the Cessna Citation X rated at 51k feet.

This is one factor that determines the max permitted altitude but certainly not the only one. E.g. another is maintaining sufficient margin to coffin corner.

In your question you asked if "certain planes" have altitude restrictions and the answer is yes. Very small or light aircraft have altitude restrictions, for example: light-sport aircraft are limited to 10,000ft MSL. As for the rest, I can guarantee you were not at 55,000ft, airliners nowadays have service ceilings (the plane physically can't climb higher, not a law) at 45,000ft max. The Concorde could cruise as high as 60,000 but it stopped flying in the early 2000s, some business jets can go up to around 50,000ft.

Welcome to aviation.SE! Do you have a source for the 10,000' limit on LSAs? As far as I know, recreational and sport pilots are limited to that altitude, not the aircraft themselves.